A variety of available blood processing systems allows for the collection and processing of particular blood components, rather than whole blood, from donors or patients. In the case of a blood donor, whole blood is drawn from the donor, a desired blood constituent isolated and collected, and the remaining blood components returned to the donor. By removing only particular constituents rather than whole blood, it takes the donor's body a shorter time period to recover to normal blood levels, thereby increasing the frequency with which the donor may donate blood. It is beneficial to increase in this manner the overall supply of blood constituents made available for health care, such as red blood cells (RBCs), leukocytes, plasma, and/or platelets, etc.
In the case of a patient who requires blood therapy, for example due to blood disease, one or more blood components may be in need of treatment. Commonly treated blood components include RBCs, leukocytes, plasma, and/or platelets, etc. In such therapies, whole blood is drawn from the patient, the problematic blood component is separated and undergone a treatment phase, and the remaining blood components and treated blood component are both returned to the patient. The treatment phase of the problematic blood component can include retaining all or a portion of the component and substituting with a suitable replacement fluid, or selectively filtering out the pathogenic compounds from the blood component with or without providing a replacement fluid.
Different disease states may implicate different components of blood. For example, two blood components commonly affected by various disease states include plasma and red blood cells. Examples of diseases that affect plasma and require plasma therapy include immune-mediated diseases, autoimmune diseases, neoplasia, infectious diseases, sepsis, cholesterolemia, organ transplant rejections, microcirculation disorders, and/or ischemic tissue damage, among many others. For a patient with a disease affecting plasma, the treatment phase of the problematic plasma can include retaining all or a portion of the plasma and substituting with a common replacement fluid such as saline, solution containing albumin, and/or donated fresh frozen plasma, or by selectively filtering out through adsorption the pathogenic compound associated with the disease state from the plasma and returning the pathogen-free plasma to the patient. In the case of selective filtration, a processing device, such as an adsorption device or column, can be used to filter out the pathogenic compound for different disease states. For example, low-density lipoprotein (LDL) and/or lipoprotein a (Lp(a)) may selectively be removed from the plasma in hypercholesterolemia cases; pathogenic antibodies removed in autoimmune disease or organ transplant rejection cases; and/or fibrinogen, fibrin, or C-reactive protein removed for microcirculation disorders or ischemic tissue damage cases.
Examples of diseases that affect RBCs and require RBC replacement therapy include sickle cell disease, ABO-incompatible bone marrow transplant cases, multiple types of anemia, malaria, protozoal infections, and/or carbon monoxide poisoning, among other such diseases that affect the red blood cells. For a patient with a disease affecting red blood cells, the treatment phase of the problematic RBCs can be a RBC exchange procedure, which typically involves retaining a substantial portion of the RBCs and substituting with healthy RBCs originating from a donor. The replacement RBCs may join with the patient's non-RBC components (e.g., plasma, leukocytes, platelets, etc.) to re-enter the patient's bloodstream. The treatment phase of the problematic RBCs can also be a RBC depletion procedure, in which greatly elevated numbers of RBCs may be reduced by rapid removal of RBCs. RBC depletion may be appropriate for disease states such as polycythemia vera and iron overload, when it becomes necessary to reduce blood viscosity, RBC volume, and/or iron load. RBC depletion may also be accompanied by fluid substitution in which appropriate replacement fluids such as saline and/or albumin replace removed volume and therefore maintain fluid balance.
The separation phase of blood components from whole blood typically takes place prior to the treatment of the problematic blood component and may be achieved through a spinning membrane or centrifugation, in which whole blood is passed through a centrifuge or membrane after it is withdrawn from the patient. To avoid contamination and possible infection of the patient, the blood is preferably contained within a sealed, sterile fluid flow system during the entire separation process. Typical blood processing systems thus may include a permanent, reusable hardware assembly containing the hardware (drive system, pumps, valve actuators, programmable controller, and the like) that pumps the blood, and a disposable, sealed and sterile fluid circuit that is mounted in cooperation on the hardware. In the case of separation via centrifugation, the hardware assembly includes a centrifuge that may engage and spin a separation chamber of the disposable fluid circuit during a blood separation step. The blood, however, may make actual contact only with the fluid circuit, which assembly may be used only once and then discarded. In the case of separation via a spinning membrane, a disposable single-use spinning membrane may be used in cooperation with the hardware assembly and disposable fluid circuit.
In the case of separation via centrifugation, as the whole blood is spun by the centrifuge, the heavier (greater specific gravity) components, such as red blood cells, move radially outwardly away from the center of rotation toward the outer or “high-G” wall of the separation chamber of the fluid circuit. The lighter (lower specific gravity) components, such as plasma, migrate toward the inner or “low-G” wall of the separation chamber. Various ones of these components can be selectively removed from the whole blood by forming appropriately located channeling seals and outlet ports in the separation chamber of the fluid circuit.
In the case of separation via a spinning membrane, whole blood may be spun within a disposable spinning membrane, rather than within a separation chamber of a fluid circuit. Larger molecules, such as red blood cells, may be retained within one side of the membrane, while the smaller molecules, such as plasma, may escape through the pores of the membrane to the other side of the membrane. Various ones of these components can be selectively removed from the whole blood by forming appropriately located outlet ports in the housing of the membrane column. Various types of columns with different pore sizes may be used, depending on the components to be separated.